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Recently I've been trying to print time series for different regions and show them in the same plot. Everything goes fine if I exclude the 4th region into the time series (1-3 time series are fine). But when I add the 4th region, time series points at other locations are gone. The output plot only shows the time series of the last region (only remains 2 points of other regions).

So the problem is: how to add the time series of the 4th region into the plot?

Excluding the 4th region in the feature collection would work properly, but I don't want to omit it.

Here's the link to the code.

var timeField = 'system:time_start';
// Define test regions.
var regions = ee.FeatureCollection([    // Test Regions are in Hunan, China.
  ee.Feature(    // Region 1
    ee.Geometry.Rectangle(113.201806473291, 27.6867096858736, 113.251537728778, 27.7276180415286), {label: 'Region1'}),
  ee.Feature(  // Region 2
    ee.Geometry.Rectangle(113.152404668942, 27.6389241071109, 113.177553060666, 27.6780758597365), {label: 'HengJiangCun'}),
  ee.Feature(  // Region3
    ee.Geometry.Rectangle(113.196381164761, 27.7769042331009, 113.216382570871, 27.7999150021881), {label: 'ChenJiaBa'}),
  ee.Feature(  // Region4 Adding this region would omit most of the points
    ee.Geometry.Rectangle(113.038857564920, 27.9581880215077, 113.042355165475, 27.9719283228899), {label: 'ZhaoShanXiang'}),
]);

// Add base maps.
Map.addLayer(regions, {}, 'Test Regions'); // Layer: Test Regions.
print(regions)

// Load Sentinel-2 TOA reflectance data.
var masked = S2                                 
    .filterDate('2017-01-01', '2017-12-31')
    .filterBounds(regions);
print(masked);

// Function to calculate NDVI in S2 images.
function S2NDVI(image){
  var bands = image.select('B4','B8');
  var NDVI = bands.expression('(b(1)-b(0))/(b(0)+b(1))').select(['B8'],['NDVI']);
  //return NDVI;
  return image.addBands(NDVI);
}

// Calculate S2 NDVI.
var S2VI = masked.map(S2NDVI);
print(S2VI);

// Generating 25 percentile time series chart.
var reducer = ee.Reducer.percentile([25]);

// Time series chart settings.
var TSChart = ui.Chart.image.seriesByRegion(
    S2VI.select('NDVI'), regions, reducer, 'NDVI', 20, 'system:time_start','label')
        .setChartType('ScatterChart')
        .setOptions({
          title: 'CI-Red Edge time series at 4 regions',
          vAxis: {title: 'CI Red Edge'},
          lineWidth: 1,
          pointSize: 4,
          series: {
            0: {color: '008744'}, // Region 1
            1: {color: '0057e7'}, // Region 2
            2: {color: 'd62d20'},  // Region 3
            3: {color: 'ffa700'}, //Region 4
}});

print(TSChart);
Map.addLayer(S2VI.select('NDVI'),{},'Sentinel VI Collection');
  • 1
    Please Edit your question to contain code, so that when the link on the third-party site fails, the question body will not be damaged. – Vince Nov 27 '18 at 1:49
  • Have you tried adding a 5th region and see how that interacts with the other 4? – whyzar Nov 27 '18 at 18:33
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This problem is similar to something I discovered. It doesn't seem good to filter an image collection on a feature collection with multiple geometries. Instead, you should use filterBounds on just one geometry, for example a point or rectangle.

I guess this has something to do with the Sentinel-2 colleciton, in which every image is divided into multiple (I think 4) granules (or 'tiles'). You will see that your image collection now consist of about 62 images, so almost 4 times less images.

When I add the following to your code, it returns the graph you probably will have expected. The point is in the middle of your four regions.

// add a point
var point = ee.Geometry.Point([113.16010429074402, 27.739383729419057]);

// Load Sentinel-2 TOA reflectance data.
var masked = S2                                 
    .filterDate('2017-01-01', '2017-12-31')
    .filterBounds(point);
print(masked);

Link to the code: https://code.earthengine.google.com/717ec998129ee7afba4e2395f1ef5edf

The new Graph

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